Several coating processes have been developed for coating patches of low to moderate viscosity, self-leveling liquids, such as liquid optically clear adhesives (LOCA composition), onto substrates. One known process for applying a liquid patch to a substrate makes use of low viscosity Newtonian coating liquids at the application conditions. To prevent flow beyond the desired printing area due to self-leveling of such low viscosity Newtonian liquids, the use of a pre-cured dam material is often required. This involves an additional process step, and may potentially lead to overflow of the coating liquid if a sufficiently precise amount is not dispensed. It is also known to perform patch coating from a slot die, with several known variations. One such variation creates a pattern of spaced discrete patches directly on the substrate by using a metering pump that intermittently supplies coating liquid to the internal cavity of an extrusion (or coating) die from a fluid reservoir. Early examples of liquid patch coating directly on a substrate achieved limited accuracy and precision in positioning of the patch on the substrate.
Recently, higher precision applications, including the coating of LOCA composition patches directly onto a substrate, have required process improvements to control the edges and the overall thickness uniformity to tight specifications. For example, the use of a screen for precise printing a liquid patch on a substrate has been described, for example in Kobayashi et al. (U.S. Patent Application Pub. No. 2009/0215351). Additionally, the use of a stencil for precise printing of LOCA composition patches has been described in PCT International Pub. No. WO 2012/036980. Such processes have been found useful for coating LOCA compositions onto substrates useful in laminating optical assemblies for producing display panels used in a variety of electronic devices.